1. Field of the Invention
The present invention relates to a digital signal recording method in which a plurality of divided segments are independently edited in the same recording track, and a drum unit for recording an FM audio signal and a digital signal with the same head.
2. Description of the Related Art
Multi-channel satellite broadcasting service is now available in the United States. In such service, multi-channel broadcasting is realized by a digital compression technique for significantly compressing video signals or audio signals. Moreover, a bit rate is changed in accordance with the contents of a broadcasting program. For example, a low bit rate (for example, 3 Mbps) is used for movies or the like, and a high bit rate (for example, 6 Mbps) is used for live broadcasting programs or the like. The similar service is being planned to be provided in Japan and Europe by using a satellite, a ground wave or a cable.
In the case where such broadcasting programs are recorded by a digital video cassette recorder (hereinafter, abbreviated as VCR), a number of programs can be recorded onto one cassette tape. Therefore, it is required that information recorded onto the cassette tape can be more precisely retrieved at a higher speed. Furthermore, as original video libraries, subcode data regions for recording not only a signal for searching the beginning and a time code of video signals recorded onto the cassette tape, but also the simplified contents of the video signals are intended for use. However, these data regions are frequently overwritten after video images are recorded therein. Moreover, it should be ensured that data is read therefrom with high speed search.
Japanese Patent Publication No. 3-30950 discloses a technique regarding the overwriting of digital data. According to this technique, when the digital data is partially overwritten, the previously recorded data to be overwritten is prevented from being left unerased. In this technique, the digital data can be erased by overwriting the data with a preamble length and a postamble length which are determined in view of synchronizing the reproducing data using a phase locked loop (PLL) and a jitter amount of a VCR.
In such conventional preamble and postamble recording/overwriting, a large preamble amount and a large postamble amount are required to prevent the interface between overwritten edited data and unedited data in a track. Therefore, if the same preamble amount and postamble amount are provided for all various data having different forms recorded in a track, a recording area of data which is effective to a user is disadvantageously limited. More specifically, it is desirable to reduce a preamble region and a postamble region as small as possible so as to increase data storage capacity. As a result, however, an unnecessary signal region is formed.
Moreover, the conditions regarding a gap are not referred to in the conventional technique.
In addition, in order to obtain the compatibility with a conventional analog VCR, a head for analog video signals, a head for FM audio signals and a head for digital signals are required to be independently provided, resulting in the increased cost of a device.